Modular shell reef for erosion abatement

ABSTRACT

The disclosed systems, methods, and apparatuses may combat coastal erosion using a shell module shaped to enable retention of sand on a beach and shore face. The shell module may be shaped to minimizing interference with recreational use of the beach and providing a beneficial environment for desirable sea life. The modular shell can be conveniently transported and emplaced in shell reefs. These shell reefs may comprise multiple, optionally interlocking shell modules. These shell reefs can prevent fill, such as sand, de-watered sand, or sand slurry from being scoured and sluiced out to sea. The disclosed systems and methods harness the energy of incoming and returning waves, including tidal and surf action, to assist in spreading the fill, recreating a natural beach, complete with layers of sand capable of resisting the scouring force of ocean waves and currents.

RELATED APPLICATIONS

This application claims the benefit of priority to Provisional Application No. 62/310,032, filed Mar. 18, 2016, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The disclosed embodiments concern systems and methods for beach erosion abatement. More specifically, the disclosed embodiments concern modular shell reefs emplaced within the surf zone to reduce scouring of a beach and the receding of the shoreline.

BACKGROUND

A beach protects the coast, normally not in contact with the ocean water, against the erosive forces of waves and currents. The coast, consisting of dunes, banks, bluffs, cliffs and similar features, is not normally in contact with the ocean. But the toe of the coast, where the coast meets the beach, may be exposed to the erosive forces of ocean waves during astronomical high tides or storm surges. The toe of the coast cannot generally withstand these erosive forces and can be scoured and sluiced away. This may undermine the coast, for example causing portions of dunes, banks, bluffs, or cliffs to collapse and leading to further erosion.

The beach is therefore the first line of defense in preventing erosion. Sand is naturally deposited on a beach cyclically in layers by the action of ocean currents, waves, and tides. These layers consist of various gradations of sand particles, clay and silt, including organic substances which add an element of cohesive strength. A natural beach generated through such deposition, with a naturally occurring elevation and gradient, can resist the scouring force of ocean waves and currents.

However, an artificial beach provides at most a temporary protective effect. Such beaches may be produced by spreading washed or de-watered sand. During the process of washing or watering, fines such as silts, clay and organic substances are flushed out. Consequently, unlike naturally deposited sand, this washed or de-watered sand lacks cohesion and will quickly be reclaimed by the ocean. Unless the washed or de-watered sand can be retained on the artificial beach, the expensive and environmentally disruptive process of mining or dredging sand, processing it, and dumping it on the artificial beach must be periodically repeated.

Armoring the coastline with revetments or similar barriers creates other problems. In part, these devices cut off the flow of sediment that nourishes other beaches. Furthermore, the swash and backwash of the incoming waves can lower the elevation of the beach, undermining and destabilizing the revetment. This may cause the revetment to fail, causing the eventual loss of the beach. Sand filled bags, tubes or containers that restrict the free movement of sand particles act as armor, similar to revetments with similar problems. The backwash can become trapped behind these barriers, causing unintended problems. Methods that armor the coastline may also be unsightly, creating opposition to these methods.

Present methods of erosion abatement are therefore expensive, environmentally disruptive, and ineffective. A need exists for improved erosion abatement techniques that retain the washed or de-watered sand on the beach for more cohesive deposition during cycles of natural beach accretion. Such techniques should also minimally interfere with recreational use of the beach, and preferably provide a beneficial environment for desirable sea life.

SUMMARY

The disclosed embodiments can include a sand-retaining shell module adapted for placement near a shoreline. This shell module can comprise two footers generally parallel to a longitudinal axis. These footers can include and outer face and an inner face. The shell module may further comprise a bridging member. The bridging member can connect the two footers, and can have a convex upper surface peaking at the longitudinal axis and extending downward on either side of the longitudinal axis to meet the outer face of each footer. The bridging member can also have a concave undersurface peaking at the longitudinal axis and extending downward on either side of the longitudinal axis to meet the inner face of each footer. The shell module, when viewed from above, may have a generally square or rectangular peripheral outline. In some embodiments, the shell module may comprise a unitary structure made with a mold.

In some embodiments, the shell module may have a first end and a second end, each generally orthogonal to the longitudinal axis. The first end can be formed with a projection and the second end can be formed with a complementary recess, enabling installation of adjacent shell modules in an interlocked configuration.

In some embodiments, the bridging member can be formed with a central portion aligned with the longitudinal axis and a perforated portion connecting the central portion and one of the two footers. The perforated portion may be formed with a plurality of slots extending from the upper surface to the undersurface of the bridging member, thereby facilitating passage of water and marine life through said module. The bridging member may reduce in thickness from at least one of the two footers to the central portion.

The disclosed embodiments can include a system for abating erosion of a shoreline. The system can include a main shell reef emplaced along the shoreline at least partially within the shore face and beyond the mean low water line. The shell reef can be formed from a plurality of adjacent shell modules. Each of the adjacent shell modules can be formed with two footers and a bridging member. The two footers can be generally parallel to a longitudinal axis of the shell module. Each footer can comprise an outer face. The bridging member can connect the footers, and can have a convex upper surface. This convex upper surface can peak at the longitudinal axis and extend downward on either side of the longitudinal axis to meet the outer face of each footer. A top of the main shell reef may be below the mean low water level. The shell modules may be placed to embed the footers of each shell module into the shore face.

In some embodiments, each footer may have an inner face, and the bridging member may have a concave undersurface peaking at the longitudinal axis and extending downward on either side of the longitudinal axis to meet the inner face of each footer.

In some embodiments, the adjacent shell modules may be formed with projections and recesses that interlock the adjacent shell modules to form the main shell reef.

In some embodiments, one or more additional shell reefs may be emplaced between the main shell reef and the mean low water line. These additional shell reefs may be angled towards the shoreline, and may be submerged below the mean low water level. The one or more additional shell reefs may contact the main shell reef.

The disclosed embodiments can include a method for abating erosion of a shoreline. This method can include the step of emplacing a main shell reef with a convex upper surface along a shoreline at least partially within a shore face and beyond the mean low water line. The top of the main shell reef may be below the mean low water level. This method can include the step of depositing fill at a location within the surf zone between the main shell reef and the toe of the coastal area.

In some embodiments, the method may further include the step of emplacing an additional shell reef between the main shell reef and the mean low water line. This additional shell reef may be angled towards the shoreline. The fill may be deposited up-drift of the additional shell reef. The additional shell reef may connect with the main shell reef. The fill may comprise at least one of sand, sand slurry, and dewatered sand slurry.

In some embodiments, the main shell reef may comprise a plurality of adjacent shell modules. The shell modules may be formed with projections and recesses that interlock the adjacent shell modules to form the main shell reef.

In some embodiments, the main shell reef may comprise a plurality of adjacent shell modules. Each shell module may be formed with two footers parallel to a longitudinal axis of the shell module. Emplacing the main shell reef may include embedding the footers of each shell module into the shore face.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosed embodiments, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings are not necessarily to scale or exhaustive. Instead, emphasis is generally placed upon illustrating the principles of the inventions described herein. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments consistent with the disclosure and together with the description, serve to explain the principles of the disclosure. In the drawings:

FIGS. 1A-1E depict five views of an exemplary modular shell for erosion abatement.

FIGS. 2A and 2B depict two exemplary configurations for interlocking modular shells for erosion abatement.

FIG. 3 depicts a top view of an exemplary system for abating erosion along a shoreline.

FIG. 4 depicts a schematic side view of a system for abating erosion along a shoreline.

FIG. 5 depicts an exemplary flowchart illustrating a method of abating erosion along a shoreline using a shell reef.

DETAILED DESCRIPTION

Reference will now be made in detail to the disclosed embodiments, examples of which are illustrated in the accompanying drawings. Wherever convenient, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

As used herein, the term “generally,” “about,” or “approximately” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, e. g., the limitations of the measurements system. For example, “generally” can mean within one or more than one standard deviation per the practice in the art. Alternatively, “generally” can mean a range of up to 20%, such as up to 10%, up to 5%, and up to 1% of a given value.

As used herein, the term “toe” means the landward end of the beach, for example where the coast meets the beach. In some instances, the toe may be at the base of a bluff or dune.

As used herein, the term “mean low water level,” or “shoreline,” means the average of all the low water heights observed at a location over a period of time. In some embodiments, this period of time can be a National Tidal Datum Epoch. The term “mean low water line” means the elevation on a coastal area at the location corresponding to the mean low water level. The mean low water level and mean low water line can be approximate, and can be measured directly or obtained from a chart datum or similar data source.

As used herein, the term “mean high water level” means the average of all the high water heights observed at a location over a period of time. In some embodiments, this period of time can be a National Tidal Datum Epoch. As used herein, the term “mean high water line” means the elevation on a coastal area at the location corresponding to the mean high water level. The mean high water level and mean high water line can be approximate, and can be measured directly or obtained from a chart datum or similar data source.

As used herein, the term “shore face” means the zone extending from the low water line beyond the end of the surf zone to the closure depth, the depth beyond which no significant longshore or cross-shore transport take place due to littoral transport processes. As these littoral transport processes depend on wave climate, the closure depth may be defined by the some measure of significant wave height. For example, the closure depth may depend on the significant wave height exceeding twelve hours per year. Significant wave height can be the mean trough to crest wave height of the highest third of waves at a location. This definition of closure depth is not intended to be limiting, and one of skill in the art would be familiar with this definition and alternative suitable definitions.

As used herein, the term “surf zone” means the zone within which waves approaching the coastline typically commence breaking. This zone may be determined based on an expected wave height, such as the significant wave height exceeding twelve hours per year.

The disclosed embodiments can include shell reefs emplaced across or along the shore face. These shell reefs may mitigate erosion caused by wave action, wind forces, hydrostatic pressure, super saturation and liquefaction. These shell reefs are configured to allow the passage of waves, which can spread fill deposited on the shore face. These shell reefs also reduce the amount of fill scoured or sluiced off the shore face and lost to further cycles of beach accretion. In this manner, the disclosed embodiments maintain the gradient of the shore face and prevent undermining of the coast.

The disclosed shell reefs can comprise multiple shell modules. FIG. 1A depicts a three-point perspective view from above of exemplary shell module 100. FIG. 1B depicts a top view of exemplary shell module 100. FIG. 1C depicts a side view of exemplary shell module 100. FIG. 1D depicts a slice through exemplary shell module 100 with the location and orientation indicated by the label “D” on FIG. 1C.

Shell module 100 may be fabricated from a heavy and corrosion-resistant material. This material can be porous. For example shell module 100 may be fabricated from a non-metallic material, such as a porous polymeric material. As an additional example, shell module 100 may be fabricated from a composite material including and one or more fillers and binders, such as a porous concrete. Such fillers may include an absorbent material that absorbs water when the shell is emplaced, counteracting buoyancy forces when submersed. For example, this filler may be activated charcoal. In some embodiments, shell module 100 may comprise a unitary structure. For example, shell module 100 may be formed using a mold. As an additional example, shell module 100 can comprise precast concrete. In some embodiments, shell module 100 may be fabricated from more than one material. For example, different components of shell module 100 (e.g., footers 110 and bridging member 120) may be fabricated from different materials. One or more of these components may be formed using a corresponding mold. The components may then be assembled. Shell module 100 may have a longitudinal axis 101 and a latitudinal axis 102.

As shown in FIG. 1B, when viewed from above shell module 100 can have a generally square or rectangular peripheral outline. The shell module can have a first end and a second end, each generally orthogonal to longitudinal axis 101 and parallel to latitudinal axis 102. In some aspects, shell module 100 can have a generally square or rectangular outline, with the addition of projections and recesses for interlocking adjacent modules. These projections and recesses can be arranged on the bridging member at the first and second ends of shell module 100. In some embodiments, shell module 100 may be approximately 3 to 10 feet wide in the direction of latitudinal axis 102. For example, shell module 100 can be approximately 4 to 7 feet wide in the direction of latitudinal axis 102. In some embodiments, shell module 100 may be approximately 4 to 15 feet long in the direction of the longitudinal axis. For example, shell module 100 can be approximately 6 to 10 feet wide in the direction of latitudinal axis 102. The height of shell module 100 may be chosen to may permit traversal by bottom-dwelling animals, such as crustaceans, and by people walking in the water. For example, shell module 100 may be approximately 1 to 4 feet high. As another example, shell module 100 may be approximately 2 to 3 feet high. In some embodiments, at least some of the upper surface of shell module 100 may be textured for better traction. For example, the upper surface of shell module 100 may be textured with a non-slip sand coating.

Shell module 100 can be formed with two footers (e.g., footer 110) connected by a bridging member 120. In some embodiments, bridging member 120 may be configured to distribute the weight of shell module 100 approximately equally between footers 110. The footers may be configured to anchor the shell module into the shore face. The footers can be formed with an outer face 111 and an inner face 113. At least one of outer face 111 and inner face 112 can be approximately flat. The height of the outer faces 111 can be less than the height of the inner faces 113. The outer faces 111 may be approximately 8 inches to 24 inches high. For example, the outer faces may be approximately 12 to 16 inches high. The inner faces may be approximately 2 to 20 inches high.

Outer faces 113 may be approximately aligned along planes angled outwards, such that the separation along the latitudinal axis between the outer faces 111 is greater at the bottom of footers 110 than at the top the footers 110. In various aspects, the outer faces 113 may be approximately parallel to each other. In some aspects, the inner face 113 of each footer 110 may approximately parallel the outer face 111 of that footer. In various aspects, the inner faces 113 may be approximately parallel to each other.

Bridging member 120 can connect footers 110 and can be configured to reduce the scouring or sluicing of fill off the shore face, while allowing the passage of water through shell module 100. As shown in FIG. 1A and FIG. 1D, in some embodiments bridging member 120 may arch between footers 110. Such arching may elevate the undersurface of bridging member 120 off the shore face, concentrating the weight of bridging member 120 on the footers 110 and reducing the amount of material required to achieve a desired shell reef height. The area underneath bridging member 120 may also provide a secure breeding and hatching environment for small aquatic forms of life.

Bridging member 120 can be configured to maintain a relative position of footers 110 that generally distributes the weight of shell module 100 evenly between footers 110 when shell module 100 is submersed. For example, bridging member 120 may be approximately bilaterally symmetric around longitudinal axis 101.

Bridging member 120 can comprise two perforated portions (e.g., perforated portion 121 and perforated portion 123) and connecting portion 125. The two perforated portions may be generally flat. The two perforated portions may each be angled approximately 20 to 40 degrees with respect to the latitudinal axis of shell module 100. For example, a perforated portion may slope downwards at a rate of approximately seven inches for every foot traveled from the longitudinal axis of shell module 100. In some embodiments, the angles of the two perforated portions may differ. For example, the angle of a perforated portion 121 may be 20 degrees and the angle of perforated portion 123 may be 30 degrees.

The two perforated portions (e.g., perforated portion 121 and perforated portion 123) may include perforations 127 extending from the upper surface of bridging member 120 to the undersurface of bridging member 120. In some embodiments, the number of perforations 127 may range from 2 to 10. In various embodiments, the number of perforations may differ between the two perforated portions. The perforations may extend from aperture on the upper surface of bridging member 120 to an aperture on the undersurface of bridging member 120. The apertures on the upper and undersurfaces of bridging member 120 may be formed as slots, rectangles, circles, ovals, or other shapes. In some embodiments, the perforated portions can be formed with perforations, such as slots, extending parallel to the first or second ends (i.e., medially to laterally, or away from the longitudinal axis). In some aspects, the upper surface apertures may be dimensioned to prevent a human hand or foot from fitting into them. These perforations can facilitate passage of water and marine life through said module.

The perforations 127 may be tapered. For example, a dimension of an aperture on the upper surface may differ for a dimension of a corresponding aperture on the undersurface. As an additional example, as shown in FIG. 1C and FIG. 1D, the dimensions of a slot in bridging member 120 may taper from a smaller value at the upper surface aperture to a larger value at the lower surface aperture. This tapering can channel water exiting shell module 100 towards the shore into a jet, causing turbulence that dislodges material (e.g., silt, sand, or shingle) and transports this material further up the shore face. This tapering can also cause water entering shell module 100 and moving away from the shore to form a spray, slowing this retreating water and enhancing deposition of material.

Connecting portion 125 can be disposed along longitudinal axis 101. In some embodiments, connecting portion 125 can be formed with a rounded top surface that offers low resistance to the movement of water over shell module 100. For example, the top surface of connecting portion 125 can be approximately parabolic. In some aspects, connecting portion 125 may comprise perforations 127. As with the perforations in perforated portion 121 and perforated portion 125, the perforations in connecting portion 125 can extend from an aperture on the upper surface to an aperture on the undersurface of bridging member 120. These perforations can be slots, rectangles circles, ovals, or other shapes.

FIG. 1E depicts a schematic of an exemplary footer, perforated portion, and connecting portion. As shown in FIG. 1E, footer 110 can be formed with an embedding portion 130. This embedding portion can be configured to penetrate into the shore face (e.g., distance 149 into the shore face). For example, embedding portion 130 can be formed with bottom surface 131 and angled surface 133. These surfaces may concentrate the weight of shell module 100, enabling it to penetrate the shore face. In some aspects, angled surface 133 can evenly distribute the weight of shell module 100. Embedding portion 130 can be configured to achieve the desired degree of penetration based on the soil bearing capacity. For example, a footer with a larger bottom surface 131, larger angled surface 133, or less-sloped angled surface 133 may be adapted for either shallower penetration into the shore face, or emplacement on soil with less weight-bearing capacity. Bottom surface 131 can be approximately flat. Bottom surface 131 can be contiguous with outer face 111 along a first edge, and can be contiguous with angled surface 133 along a second edge. Angled surface 133 can be approximately flat. Angled surface 133 can be contiguous with bottom surface 131, and can be contiguous with inner face 113. In some aspects, angled surface 133 may be parallel to the upper surface 145 of bridging member 120. This may allow stacking of multiple units of shell module 100. For example, when one shell module is placed atop another shell module, angled surface 133 of the top module may sit approximately flush with the upper surface 145 of the lower module.

In some embodiments, bridging member 120 may increase in thickness from the longitudinal axis to the footer. For example, the perforated portions (e.g., perforated portion 121) can increase in thickness from a first thickness 135 proximate to the connecting portion 110 to a second thickness 137 proximate to the footer. In various embodiments, the thickness of bridging member 120 may be approximately constant from the longitudinal axis to the footer.

As described above, bridging member 120 can arch between footers 110. In some embodiments, bridging member 120 can have a convex upper surface 145. This convex upper surface 145 may peak at longitudinal axis 101. As shown in FIG. 1E, this convex upper surface 145 can extend downward to footers 110, meeting outer face 111. In some embodiments, bridging member 120 can have a concave undersurface 147. This concave undersurface 147 may peak at longitudinal axis 101. As shown in FIG. 1E, this concave undersurface 147 can extend downward to footers 110, meeting inner face 113. In some embodiments, one or more of upper surface 145 and undersurface 147 can be approximately hemispherical.

FIG. 2A and FIG. 2B depict schematics of interlocking adjacent shell modules, consistent with disclosed embodiments. As described above, the shell modules may be formed with a first end having a projection and a second end forming a complementary recess, enabling installation of adjacent shells in an interlocked configuration.

Shell module 100 a comprises a tongue and slot interlock 200 a formed by a projection on a first module interlocking with a recess on a second module. Projection 220 a can be aligned with longitudinal axis 101, and can be formed with a variety of shapes. As shown in FIG. 2A, projection 220 a may have a generally trapezoidal peripheral outline. Alternatively, projection 220 a may have a generally semicircular peripheral outline, or generally rectangular peripheral outline. As shown in FIG. 2A, recess 210 a may be formed with a shape complementary to projection 220 a. Shell module 100 b comprises a multi-projection interlock 200 b formed by a projection and a recess on a first module interlocking with a projection and a recess on a second module. The projections, such as projection 220 b, can be offset from longitudinal axis 101, and can be formed with a variety of shapes. As shown in FIG. 2B, the projections, such as projection 220 b, may have a generally rectangular peripheral outline. Alternatively, the projections may have a generally semicircular peripheral outline, or generally trapezoidal peripheral outline. As shown in FIG. 2B, the interlocking recesses, such as recess 210 b may be formed with shapes complementary to their corresponding projections, such as projection 220 b.

FIG. 3 depicts a top view of an exemplary system 300 for abating erosion along a shoreline, consistent with disclosed embodiments. As shown in FIG. 3, different portions of the coastal area may be described by toe 301, mean high water level 303, mean low water level 305, the outer boundary of the surf zone 307, and the outer boundary of the shore face 309. As depicted, surf zone boundary 307 is nearer the shoreline than shore face boundary 309. As would be appreciated by one of skill in the art, the location of surf zone boundary 307 will depend on the current conditions, and may be further from the shoreline than shore face boundary 309. For example, during periods of low tide and high waves, surf zone boundary 307 may be further from the shoreline than shore face boundary 309.

System 300 can include main reef 310 emplaced along a shoreline. Main reef 310 can be emplaced at least partially within the shore face, between mean low water line 305 and shore face boundary 309. As shown in FIG. 3, main reef 310 can be emplaced entirely within the shore face. The separation between the shoreline and main reef 310 may be fixed, or may vary. In some embodiments, at least some of main reef 310 can be emplaced at a distance from the shoreline dependent upon the characteristics of the shoreline at that point. These characteristics may include the composition of the shore face (e.g., silt, sand, or shingle), the difference between mean high tide and mean low tide, and the slope of the shore face. For example, such portions of main reef 310 may be emplaced nearer the shoreline when the slope of the shore face is greater. In some embodiments, at least some of main reef 310 can be emplaced in a straight line, or angled towards or away from the shoreline, resulting in a varying distance between main reef 310 and the shoreline.

System 300 can include one or more additional reefs 320. These additional reefs can be emplaced within the shore face. Additional reefs 320 may be angled towards the shoreline. For example, FIG. 3 depicts two additional reefs angled at approximately right angles to the shoreline. One of skill in the art would appreciated that additional reefs 320 can be emplaced at other angles, and the configuration depict is not intended to be limiting. Furthermore, should system 300 include multiple additional reefs, these additional reefs may be emplaced at differing angles. In some embodiments, additional reefs may be separated by between 40 and 120 feet. For example, additional reefs may be separated by approximately 80 feet.

As shown in FIG. 3, in some embodiments the additional reefs may approximately contact main reef 310. For example, each of additional reefs 320 may be emplaced with an end of the additional reef in physical contact with main reef 310, or within two feet of main reef 310. In various embodiments, one or more of additional reefs 320 may be separated from the main reef. For example, the additional reef may be emplaced with an end of the additional reef separated from main reef 310 by at least two feet.

As shown in FIG. 3, in some embodiments, main reef 310 and/or additional reefs 320 can comprise a plurality of adjacent shell modules, as described above with regards to FIGS. 1A-2B. In various embodiments, at least some of these adjacent shell modules can generally contact each other, as shown in FIG. 3. For example, the ends of these contacting adjacent shell modules can be in physical contact, or within two feet of each other. In various embodiments, least some of these adjacent shell modules can interlock, as shown in FIG. 2A and FIG. 2B.

Consistent with disclosed embodiments, shell modules comprising main reef 310 may differ in at least one dimension from shell modules comprising the at least one additional reef. For example, the shell modules comprising main reef 310 can be wider, longer, or higher than the shell modules comprising the at least one additional reef. As an additional example, lower component shell modules may allow the additional reef to angle towards the shoreline while remaining below the mean low water level, while shorter and/or narrower component shell modules may enable the emplacement of the at least one adjacent reef to better follow the slope of the shore face.

FIG. 4 depicts a profile view of the exemplary system 300 for abating erosion along a shoreline, consistent with disclosed embodiments. As shown in FIG. 4, coastal area 400 may include beach 410, extending from toe 301 to mean high water level 303, shore face 403, extending from low water level 305 to shore face boundary 309, and surf zone 405, extending from high water line 303 to surf zone boundary 307. As described above with regard to FIG. 3, system 300 may comprise main reef 310. Main reef 310 may be emplaced at least partially within shore face 403, and may be emplaced along the shoreline. Main reef 310 may be emplaced such that the top of main reef 310 is below the mean lower water level.

In some embodiments, as shown in FIG. 4, system 300 may comprise one or more additional reefs 310. As described above with regard to FIG. 3, these additional reefs may be emplaced between main shell reef 310 and mean low water line 305. In some embodiments, the one or more additional shell reefs can be submerged below the mean low water level 409.

In some embodiments, fill 410 can be deposited on the landward side of main reef 310. For example, fill 410 can be deposited in surf zone 405 between mean high water line 303 and main reef 310. Alternatively or additionally, fill 410 may be deposited on beach 401 within the run-up limit (the extent of swash). Fill 410 can include one or more of silt, sand, sand slurry, de-watered sand, or other beach nourishment materials known to one of skill in the art. Fill 410 can be deposited by one or more of pumping fill into position or dumping fill into position, or another method known to one of skill in the art. In some embodiments, fill 410 may be deposited up-drift of any additional reef, so that the longshore current carries fill 410 toward the additional reefs.

Consistent with disclosed embodiments, system 300 can abate erosion of the shore face. As shown in FIG. 4, main reef 310 can support a decreased slope 420 in coastal area 400 between the emplacement location of main reef 310 and beach 401. Main reef 310 can anchor this decreased slope, decreasing backwash and preventing currents and/or waves from scouring or sluicing fill 410 away from the beach, where it would be lost to cycles of beach accretion. Main reef 310 can also allow waves to continue spreading fill 410 onto beach 401 and shore face 403, enabling accretion of beach 401 in naturally cohesive layers. Main reef 310 can also enable deposition of fill beyond the emplacement location of main reef 310. Such additional deposits 430 can further anchor main reef 310 into the shore face and additionally protect the coastal area.

FIG. 5 depicts an exemplary flowchart illustrating a method of abating erosion along a shoreline using a shell reef, consistent with disclosed embodiments. After initial step 501, the method may comprise determination of the placement of the shell reef in step 503. This determination may depend on information regarding the coastal area along which the shell reef will be emplaced. For example, this determination may depend upon the composition of the share face (e.g., silt, sand, shingle, or other material), the mean low water level, the mean high water level, and the outer boundaries of the surf zone and the sea face. This information may be obtained by direct measurements according to methods known to one of skill in the art, or from charts or databases of coastal data. This determination may also depend upon the desired goals of the erosion abatement operation. For example, this determination may depend upon the desired slope of the resulting shore face following emplacement of the shell reef. As an additional example, a lesser slope may require a bigger shell reef, placed further out from the shoreline. Creation of a lesser slope may also require emplacement of additional reefs, as described above with regards to FIG. 3 and FIG. 4. Additional reefs may also be required when the beach nourishment is intended to be confined to a particular region of the coastline.

The characteristics determined may include the length of the main reef, the separation of the main reef from the shoreline, and the dimensions of the main reef. In some embodiments, these characteristics may also include the dimensions of a plurality of shell modules comprising the shell reef. Additionally, these characteristics may further include determining whether adjacent shell modules interlock, and the arrangement of projections and recesses between adjacent, interlocking shell modules. The characteristics determined may also include the fill type and transport method.

The shell reef may be constructed in step 505 according to the placement characteristics determined in step 503. In some embodiments, modules may be transported to the emplacement location on a vessel, such as a barge, or using a motor vehicle, such as a semitrailer. In some embodiments, constructing the shell reef may comprise emplacing shell modules to form a main shell reef. In various embodiments, constructing the shell reef may comprise emplacing shell modules to form one or more additional shell reefs. These shell modules may have the configuration described above with regards to FIG. 1A to FIG. 2B and may be emplaced to form an erosion abatement system such as system 300, described above with regard to FIG. 3 and FIG. 4. Construction of the shell reefs may be accomplished with construction equipment such as cranes, helicopters, bulldozers, barges, or similar equipment known to one of skill in the art according to methods known to one of skill in the art. Construction may be accomplished while minimizing use of heavy construction equipment on the beach. For example, components of the shell reef may be transported using one or more barges and emplaced using one or more crane vessels and/or helicopters. In some embodiments, component shell reefs may be placed to embedding at least a portion of footers 110 into the shore face. The degree of embedding may be predetermined or dependent upon the characteristics of the shore face at the location of emplacement. For example, the degree of embedding may depend upon the orientation of outer face 111, the orientation of angled surface 133, and the extent of bottom surface 131.

Fill may be deposited at a location between the toe of the coastal area and the shell reef in step 507, as shown in FIG. 4. For example, fill may be deposited in the surf zone between the beach and the shell reef. As an additional example, fill may be deposited on the beach within the run-up zone, where swash from breaking waves may spread the fill over the beach. In embodiments including additional reefs, the fill may be deposited up-drift of the shell reef. The fill may include silt, sand, sand slurry, de-watered sand, or other materials known in the art for beach nourishment. The fill may be deposited by pumping. For example, slurry may be conveyed using a pipeline from a dredging barge to the fill deposit location. The fill may be deposited by dumping. For example, fill may be conveyed by barge or truck to the fill deposit location. As would be understood by one of skill in the art, the particular method of depositing the fill is not intended to be limiting. After step 507, the method can proceed to an end 509.

Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed embodiments disclosed herein. Moreover, while illustrative embodiments have been described herein, the scope includes any and all embodiments having equivalent elements, modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations or alterations based on the present disclosure. The elements in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive. Further, the steps of the disclosed methods can be modified in any manner, including by reordering steps or inserting or deleting steps. It is intended, therefore, that the specification and examples be considered as example only, with a true scope and spirit being indicated by the following claims and their full scope of equivalents. 

What is claimed is:
 1. A sand-retaining shell module adapted for placement near a shoreline, comprising: two footers (110) generally parallel to a longitudinal axis, each footer comprising outer face (111) and an inner face (113); and a bridging member (120) that connects the two footers, wherein the bridging member has a convex upper surface (145) peaking at the longitudinal axis and extending downward on either side of the longitudinal axis to meet the outer face of each footer, and a concave undersurface (147) peaking at the longitudinal axis and extending downward on either side of the longitudinal axis to meet the inner face of each footer.
 2. The sand-retaining shell module of claim 1, wherein the shell module, when viewed from above, has a generally square or rectangular peripheral outline.
 3. The sand-retaining shell module of claim 1, wherein the shell module has a first end and a second end, each generally orthogonal to the longitudinal axis.
 4. The sand-retaining shell module of claim 3, wherein the first end is formed with a projection and the second end is formed with a complementary recess, enabling installation of adjacent shell modules in an interlocked configuration.
 5. The sand-retaining shell module of claim 1, wherein the bridging member is formed with a central portion aligned with the longitudinal axis and a perforated portion connecting the central portion and one of the two footers.
 6. The sand-retaining shell module of claim 5, wherein the perforated portion is formed with a plurality of slots extending from the upper surface to the undersurface of the bridging member, thereby facilitating passage of water and marine life through said module.
 7. The sand-retaining shell module of claim 5, wherein the bridging member reduces in thickness from at least one of the two footers to the central portion.
 8. The sand-retaining shell module of claim 1, wherein the shell module comprises a unitary structure made with a mold.
 9. A system for abating erosion of a shoreline, comprising: a main shell reef (310) emplaced along the shoreline at least partially within the shore face (403) and beyond the mean low water line (305), the shell reef comprising a plurality of adjacent shell modules (100); and wherein each of the adjacent shell modules comprises: two footers (110) generally parallel to a longitudinal axis (101), each footer comprising an outer face (111), and a bridging member (120) connecting the footers, wherein the bridging member has a convex upper surface (145) peaking at the longitudinal axis and extending downward on either side of the longitudinal axis to meet the outer face of each footer.
 10. The system of claim 9, wherein a top of the main shell reef is below the mean low water level.
 11. The system of claim 9, wherein each footer comprises an inner face, and wherein the bridging member has a concave undersurface peaking at the longitudinal axis and extending downward on either side of the longitudinal axis to meet the inner face of each footer.
 12. The system of claim 9, wherein the adjacent shell modules are formed with projections and recesses that interlock the adjacent shell modules to form the main shell reef.
 13. The system of claim 8, wherein the shell modules are placed to embed the footers of each shell module into the shore face.
 14. The system of claim 9, further comprising one or more additional shell reefs emplaced between the main shell reef and the mean low water line, the one or more additional shell reefs angled towards the shoreline, the one or more additional shell reefs submerged below the mean low water level.
 15. The system of claim 14, wherein each of the one or more additional shell reefs contacts the main shell reef.
 16. A method for abating erosion of a shoreline comprising: emplacing a main shell reef (310) with a convex upper surface along a shoreline at least partially within a shore face (403) and beyond the mean low water line (305), a top of the main shell reef below the mean low water level (409); and depositing fill (410) at a location within the surf zone (405) between the main shell reef and the toe (301).
 17. The method of claim 16, further comprising emplacing an additional shell reef between the main shell reef and the mean low water line, the additional shell reef angled towards the shoreline, and wherein the location is up-drift of the additional shell reef.
 18. The method of claim 16, wherein the additional shell reef connects with the main shell reef.
 19. The method of claim 16, wherein the fill comprises at least one of sand, sand slurry, and dewatered sand slurry.
 20. The method of claim 16, wherein the main shell reef comprises a plurality of adjacent shell modules formed with projections and recesses that interlock the adjacent shell modules to form the main shell reef.
 21. The method of claim 16, wherein the main shell reef comprises a plurality of adjacent shell modules, each shell module formed with two footers parallel to a longitudinal axis of the shell module, and wherein emplacing the main shell reef comprises embedding the footers of each shell module into the shore face. 